Assemblies in reaction chambers generally may allow for lateral adjustment and leveling of a wafer lift mechanism. A wafer is disposed on a wafer holder, which may have a heating element. The lateral adjustment allows for horizontal centering of a wafer within the reaction chamber. The lateral adjustment takes place by using independent x-y adjustment block assemblies. For systems with multiple reaction chambers, the lateral adjustment is duplicated for each reaction chamber to center and level the wafer holder.
With respect to leveling of the wafer lift mechanism, leveling ensures that a wafer disposed on the wafer lift mechanism is as flat as possible and parallel to a showerhead disposed above the wafer. The leveling is accomplished through a tripod leveling system. The tripod leveling system includes a three point leveling system with ports to impart pressure onto the wafer to allow for a desired flat position of the wafer. The heater is leveled by the tripod (3-point adjustment) and the tripod is ‘carried’ by the lateral adjusting plate so that centering can be accomplished after leveling. This is due to the fact that leveling will change the position of the heater platen relative to the chamber circular bore. These systems usually have an individual wafer lift mechanisms for each reaction chamber.
Reaction systems exist with multiple chambers to allow for different processing steps. For some of these systems, each chamber may have its own wafer lift mechanism. However, multiple individual wafer lift mechanisms have a disadvantage as each individual lift mechanism incurs significant capital costs. In addition, the cost may rise due to maintenance of each individual wafer lift mechanism. Individual lifts have the following additional disadvantages: (1) More complex software checks are required for motion to occur, slowing throughput; (2) Imprecise motion matching due to manufacturing variances and tolerance stack-ups; (3) Component stack-up due to multiple identical parts requirements and the supporting cables/hoses required for actuation; (4) Multiplied opportunities for sensor failure with a lack of system redundancy (a ‘master’ lift assembly can have multiple redundant sensors if needed and can be easily recovered from a motion sensor error); and (5) Longer system down-time during maintenance due to repetitive setups being required for each chamber and its motion system.
Furthermore, certain applications may require a chamber to be split into separate sections or cavities. While it may be possible to have individual wafer lift mechanisms for each cavity, the cost issues described above and potential spacing issues may not make this feasible. Prior approaches to this issue have utilized a series of tunnels and gas distribution systems to raise separate wafer holders. Other approaches include certain ‘carousel’ systems that have been used in Physical Vapor Deposition (PVD) ‘sputtering’ applications with satisfactory results. These same methods were not as suited for Chemical Vapor Deposition (CVD) and its variant methods including Plasma-enhanced CVD (PECVD) and Atomic Layer Deposition (ALD). These last systems have been the driving force for multiple-wafer processing in matched-chamber environments to regain the throughput lost to PVD systems.
In addition, for multiple cavity systems, another issue with multiple individual wafer lift mechanisms is the reproducibility of reaction conditions. In certain applications, precise chamber matching may be required to allow for process duplication between different cavities. Merely disposing two wafer holders for two cavities on a single wafer lift mechanism may be insufficient because discrepancies with the vertical positions of the two wafer holders may exist as a result of a tolerance stack-up.
A tolerance stack-up is known in the art as an aggregation of mechanical variances within dimensions of various parts within an assembly, resulting in a minimum and maximum value range of variations. An aggregate variation can be great enough to affect the reproducibility of conditions within different cavities. This could potentially lead to defects in manufacturing, as well as decreased chamber life due to deposition material ‘leakage’ into non-process regions of the chamber. As a result, a need exists for a system that allows for the matching of vertical positions in multiple separate cavities of a reaction chamber.